Halogen-metal exchange in ortho-dibromobenzene 1 using four equivalents of tert-butyl lithium (t-BuLi) in Et₂O:THF (1:1) at -120° C was observed to yield ortho-difunctionalized benzenes 2 after quenching with an excess of electrophiles based on analysis by GC/MS.

Two reaction pathways are conceivable. The thermally unstable ortho-lithiobromobenzene 3 formed in the first exchange step could again be lithiated to give ortho-dilithiobenzene 4 (path A). Our trapping studies with electrophiles of differing reactivities show that a successive exchange-functionalisation mechanism (path B) through 5 and 6 is operating.

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1. Boron and Boron-Nitrogen Analoga of Organic Reactive Intermediates